Despite being the second in the line of succession, Prince William has been training with Queen Elizabeth II from a young age in order to become a good head of the monarchy. Although William is now a very good prospect in terms of leadership, the Queen and the rest of the royal family once had doubt about the young William, fearing that his inability to keep himself calm under pressure would jeopardize his capability to rule as a monarch.

This fear by the Queen and the royal family rooted from Princess Diana’s behavior after her separation from Prince Charles. In a shocking 1995 Panorama interview, Diana revealed the difficulties of being a king and detailed how daunting a task it would be for anyone who would undertake it.

The interview left many of the members of the royal family astounded and furious, causing some doubt upon Diana’s ability to mentor the young prince for his future role as king. “It was no secret that towards the end of her life, reactionary elements in the establishment were questioning her desirability as a mentor in the art of kingship,” said Diana’s secretary, Patrick Jepherson.

“The one person who could help [William], who had to help, was the Queen,” wrote royal biographer and expert Ingrid Seward in her book “My Husband And I: The Inside Story Of 70 Years Of The Royal Marriage. “She knew only too well what pressures William was facing. She told her advisors she feared he might crack up like his mother had.”

Thus, the Queen decided to step in, mentoring the 13-year-old boy and teaching him the duties and responsibilities of being part of royalty. Princess Diana and Prince Charles’ separation caused the Queen and William to barely see each other, and the Queen felt “great sadness” over this. Setting regular “lunch dates” with William, she had once again found an avenue to spend time and reconnect with her grandson.

“They talked in a way they never could have done before,” Seward continued. “One of her great sadnesses was that, until the separation, she had hardly seen him. Now, at last, she was able to do so on a regular basis and form a proper relationship. In this quiet intimacy, the Queen was able to impress upon William that the institution of the monarchy was something to be upheld and respected, and worth preserving.”

Princess Diana, Prince Harry and Prince William Princess Diana (L), Prince Harry, (C) and Prince William (R) gather for the commemorations of VJ Day, 19 August 1995, in London. JOHNNY EGGITT/AFP/Getty Images